Variable-speed polyphase motor.



PATENTED DEC. 25, 1906.

v R. 1). MERSHON.

VARIABLE SPEED POLYPHASE MOTOR.

APPLICATION FILED 8EPT23,1903.

D. Ji /"sham [lei/awful "RALPH nfMnnsHou.

" .'OFFIC.

or NEW YORK, 1v. Y.

VARIABLE-SPEED PO LYPHAS E MOTOR.

To (LZZ whom it nanny (Io/warn:

Be it known that I, RALPH D. MERsHoN, a citizen of the United States, residing at New York, in the county and State of New York, "shave invented certain new and useful Improvements inVariableSpeed Polyphase Motors, of which the following is a specification, f reference beingh'ad to the drawings accompanying and forming a part of the same. R. My present invention relates to systems of. power transmission by alternating currents, *and has for its object toprovide a practicable'and efficient motor capable of running at varying speeds on a circuit supplying al-g 1'5 ternatmg currents of unvarying frequency.

fln'asmuch as such a motor haslong beendesired, it may be advantageous to examine "fbriefly the present state of the art before explaining specifically the nature of my invention. 4 'The chief obstacle, if not 'ractically the only obstacle, to the use of a ternating-cur rent motors where direct-current machines, are-now employed is the fact that at present known to the artthere'is no method of varying thespeed of an a]ternating-currentinotor which does not possess serious defects. I In operating railways, elevators, and other apparatus in which considerable ariation of i speed'necesssary or desirable the directeurrent motor. is now almost universally used,'although in. many other respects the alternating-current motor is preferable. A y number of ways have been proposed and to some extent used for obtaining thecapability of speed variation so-imuch desired. One T method is to use a rheostatinthe secondary in the well-known manner. This secures the i desired result, but with such a loss in the. 4o 'efliciency of the alternating-current motor as ',.to render the plan. objectionable. Another .method, known as concatenated control, "sometimes used where two or more motors are-connected to the same load but in. this case a rheostat must be -employed with at least one of the motors. Still another method is to vary the number of poles in the errorgizing-circuits, with corresponding change of (speed; but as hi-aretoforepracticed the loss I59 inefficiency by this method may beso great as to be prohibitive. Hecmirse'must thereforeg'enerally be had to direct-current niachines, although, as before stated, the alter- 7 Hating-current motor is in many, other respects superior. I r In some cases the necessity of using direct- Specification of Letters Patent. Application filed September 22, 1903. semi No. 174,274.

tant water-power or othersource.

. constructed and operated according) invention, however, Wlll be found to 'eration is tln-u'efore preserved.

to the proper point.

Patented Dec 25,1906.

current motors becomes particularly objectionable, as'when power is to be transmitted over long distances, over a system of distribution many miles in extent, or from a dissuch conditions it is necessary to generate alternating current, transmitit athi h tension to the point of utilization, and en by means of costly apparatusand attendance convert it into direct current...- The power must be transmitted by alterhating, current,

since with direct current the loss inytransmission would be enormous unless the'conductors were impracticably large or expensive. Havin by means of the efiicientand economical a ternating apparatus delivered the power to the point where it is to be utilized, the current must then be rectified, with a resulting loss of a large proportion of the previous saving, merely because alternating-current motors do not possess that practical capability pensable. Y

To avoid the necessity and consequent-expense of rectifying-the current, a system has 7 been proposed, particularly for use in eonnection with railways, in which the alternating current from the line encr izes a motor on the locomotive or car, whic in turn drives a generator also on'the. car. 'Currentfrom the latter generator is then suppliedto-a' second motor, also on the car, which in turn propels the vehicle. This plan has-advantag-es for certain purposes {but at best it ,always requires three maoln'nes to do the'work of one on each propellingwehicle. :A n otor to my ble of speed control as readily as a direct' current machine, without the defects 'of the lat-- ter, and to possess none of the objectionable features found in lJllG'PIBVlOUS methods of Of speed control which is so indis Under f var in the s eed of an alternatin current motor. At the same time the-invention possesses numerous positive advantages. 7 In the first place, since-it 1s operated by altermating currents the use of rotary converters and their maintenance are dispensed with and the economy of alter11atingei 1rrent gen- 'In long-dis tanee transmission the only intermediateap paratusrequirod is the transformer vor transformers necessary to step downfthevoltage Again, no rheostat is used, and thereis therefore no rheostatic loss W'hen rhe motor is running at less. than normal speed. For example, in bringing the {is that of a non-u'niformly-distributed windmo'tor and its load from rest to maximum speed or in running at any speed less than maximum there is .no loss of power in the rheostat, and the motor at an intermediate s eed, as well as at maximum, consumes aproximately on'lyso much power as is required to carry the load at that particular spec A further advantage, and one of the mostimportant, is the economy effected in stopping the load or bringing it from a 'lhigher to a lower speed. In such cases the iiznertia of the moving masses or, statedotherwise. the kinetic energy stored in the load, instead -of being wasted in the brakes is transformed into electrical energy by the -mo :tor .and is delivered to the supply-circuit zt0 be utilized by other motors or translating devices connected therewith. This feature of the invention is of special value in traction systems where heavy trains with (enormous inertia have to be brought from high speed :to a-stop. The potential nergy ofthe load'i-s also transformed into eliectrical (energy and delivered to the .-lineas, for example, in the case-of atrain running downgrade, Here, ,as before, instead of applying the brakes to keep, down 10.1 reduce .the speed the motor itself receives the energy and returns 'itto the supply-circuit. Another instance which may he mentioned in this connection is a descending elevator-car. Here the potential energy, which is not inconsiderablc, may be -;utilized :to aid in raisingother cars. In fact, it may be said generally that the motor will consume a proximately only enough powerto carry t e load at the desired speed, whatever that may be, and that when from any cause the load itself is-developing power the same may be transformed into useful ener y and returned to the supply-circuit instea 'of being wasted, as is now commonly athe-case.

'In .order :to utilize the principle of varying the number of poles .to secure a variable speed .in :motors of the type referred .to, and

more especially in ipolyphase induction-mo tom :or those having closed secondary wind-- ings, I'haye found it mecessary to make special provisions'for maintainingthe field of approximately con st ant strength-and in uniform rotation without regard to :the number of .poles.

In general practice, with the number of phases usually available from the ordinary sources of supply and when the speed of the nnotor is not -to be varied, the condition of approximately constant strength and uniform rotation of the iield of the latter is at :tainec'l or approximated either by groi zping the primary or held windings so that their distribution is not uniform or by winding the'coi'ls in the case of a drum-winding with a pitch greater or less than one hundred and eighty electrical degrees, so that their effect ing. All such windings 1 shall hereinafter designate as non-uniformly distributed, but a non-uniformly distributed winding does not readily lend itself to the plan of varying the number of poles by varying the points of connection of each phase, since a distribution which suits one number of poles may not be at all suitable for another. For one number of poles such a winding may give a uniformly-rotating and approximately constant field, while for other numbers this result may not beobtained, and if :the endeavor is made, as has been frequently the case, etO

rearrange by a commutator or controller the connections of the various coils of the winding simultaneously with the change in the points of connection of the phase the result is an objectionable complication, in addition to the fact that for low speeds, and therefore a great number of oles, the distribution of the winding will be ess effective for uniformity of field, because the number of coils per pole is greatly reduced. My im rovement, owever, although in generalapp icable with the best results to a uniformly-distributed Winding, applies also to one which is not uniform and overcomes the practical objections to the plan heretofore proposed, for While any improvement contemplates a greater number of anziin leads to the motor than in the case of aunotor whose non-uniform winding is conymutatedas above described, there is no commutation of the windings of the motor itself, but merely a change in .the points of connection of the main leads to the .motor, the result 'beinp'greater simplicity both in the construction of the motor and in the meals of making the required changes of connec- Ition. Forlconvemence the invention will be described as applied to a uniformly-distributed winding and tea motor whose numberof poles may be made either two or four. The

same desoriptionfhowever, would apply if the windings of the motor be assumed to :be non-uniform instead-ofuni-form, as shown in the drawings.

In illustration of the principle of the invention let aiuniformly-distributed winding having an infinite number of turns to which an infinite number of phases is supplied be assumed. The resulting field will be absolutel y constant in value and uniformly rotating. 1n like manner if a large number of phases be supplied to a uniformly-distributed winding of a 'iinite number of turns the resulting field will be approximately constant in value and uniform in rotation, the degree ofapproximation depending upon the numberof' phases employed. I therefore propose; primarily, to operate the motor by supplying to it aconsiderablc number of phases;

but as it would not be practicable to obtain those directly from the source of supply. 1 propose. to use in connection with the ord1- nary two or three phase supply-circuits a .polyphase transformer or a plurality of single-phase transformers so disposed or whose windings are of Such'aeharacter or so interconnected'as to yield-.anumber of phases as much in excess of that of the main or supply circuit as may be desired. I

By using a large number of phases 1 obtain with a unifornily-distributed winding all .Ie the advantages of a non-iuniformly-distr'ibuted winding without any of its objections, since for each number of poles-which the special connections may produce Iobtain all the advantages as regards uniformityof field l 5 that would be sebured by a winding non uni, formly distributed with reference to each number of'poles, and by supplying ,the greater number of phases to a non-uniformlydistributed .-Winding. I attain the result in :o,..carrving out my invention for which such g is primarily employed that is/for securing uniformity of field-and this without the drawbacks previously mentioned. The methods of obtaining a number of 5 phases different from that of the supply-circuitare various and well known. or example, by the'.. intereom1'ection of the two transformers four phases (quartenphase) Iywbe obtained from a three phase source, ythree transformers not interconnected ilgphase's may" beobtain'ed from a three- "phase' source. ,Again, by the use of two transformers with primaries interconnected l to transform from three phaseor two non- 3 5 interconnected transformers transforming from two phase and in the cores of which, therefore, the fluxeswill be in quadrature and windingv upon their "coresthe requisite 1 number of secondary coils of the proper num- 40 berof turns'it is possible by interconnecting the various'secondaries of the two to obtain as many phases as desired and of any voltage desired; This follows from the general conrf-sideration that since the two transformers 15 will yield eleetromotive forces ninety degrees apart and since any electromotive force "may be resolved into .two components along any two axes ninety degrees apart we may by combining; two electrol'notive forces of the' proper relative values, one of which is obtamed fw'fn one of the transformers and the other from the other transformer, obtain value desired; I

The drawings hereto annexed illustrate r diagrammatically in Figure 1. the arrangementof circuits'and apparatus necessary for practicing my invention on the assumption that five phases will be supplied to themotor ,electromotive force of any phase and any and that they will be obtained by compound- 7 ing electroinotive forces in quadrature. Fig.

2-is a vectorial diagram showing the amount anddirection of the components which must be -taken from each of the quadrature com- 552 ponents to obtain anypne of the fivephases.

i G indicates a source of polyphase current which is assumed in this case to be threephase, and M an alternatng-current motor of any suitable characte1 --for example, one

maries of which are intercom:ec'tcd in thewell-known manner indicated; so that when supplied Wltll currents from' a three-phase source the'fluxes in'the cores w ll differ by ninety degrees. Two transformers might be used the fluxes in whose coresare at some otherangle than ninety degrees providedthe windings of the transformers were so proportioned and connected in the manner well known to those skilled in 'theiart as to be adapted to the angle which exists'between the fluxes i v i The motor here shown is tobe operated with either two or four poles, thus giving two speeds It is supplied with iive-phasecnrrents through fiv eads h, i, j; 7c, and Zfrom the secondaries f 'f"ff'-f and 917" g" g of the transformers D andEQ The derivation of five phases from the three supplied to the transformers will be more readilyunderstood inconnec'tionwith Fig, 2-. The secondaries f f f" f? f supply -electromotive forces which may be considered as being those corresponding to A, and A, of thelast-nientioned' figure, since A, and-A differ by one hundred and eighty degrees and may therefore be obtained from the same transformer, but from separate secondaries whose connections are the reverse one of the other. Similarly, the co ls g 9 9 9 may be taken as corresponding to the electromotive forcesJi B It w ll be seen by following out the connections of the various secondaries that the quadrature components of (-dectromotivc force are'conn bined in the manner and with the results in dicated in F g. 2. The secondary co ls are all shown as having the same number of turns, a tap being taken oil at the proper point to obtain the required value for the component of electromotivc force, although in practice only so inuch of the coil as is required would be wound uponthe core.

The relation between the transformer-dim grain in l*"g. 1 and the vectorial diagram of F 2 having now been explained, the latter figure \Vill be readily understood. Therein is shown the relation of the electromotive forces in r 1-1adrature--A for one phase and B B, for the other and the five phases .1 2 3 4 5, whiehare to be obtained from them.

The diagram shows one of the numerous methods in which the quadrature electrometive forcesmay be obtained to obtain the five phases, and the electromotive-force parallelograms completed by the dotted lines indicate the amount and direction of the components which must be taken from each quadrature ele'ctromotive force to obtain any one oi the five phases. For example, phase 1 is obtained directly from the electromotive force A, without composition. Phase 3 is obtained by taking a certain proport on, as shown in the diagram, of B, and A and compounding them, and so on for the other phases.

As will be seen in Fig. 1, only five leads are brought from the interconnected secondaries; but diilerent voltages can nevertheless be delivered by varying the primary connections, as will be readily understood. For this purpcsea controller N is provided; (Diagraminatically illustrated in Fig. 1.) I The lower voltage is used when the motor is run with the greater number of poles and the higher when run with the lower number. In general, it will usually be desirable to decrease the vol tage as the number of poles is increased' Variation in voltage impressed uponthe motor may also be accomplished by bringing out additional leads from the secondary coils instead of from the primaries, the different leads supplying the different voltages.

A controller of any suitable character may be employed in connection with the motor, and to it the various leads from the inter connected secondaries are brought. In illustration of this I have shown by projection in the flat a cylinder of insulatingn aterial 'H, bearing two rows of contacts or terminals K L. It is assurr ed that by turning, the cylinder H either row of contacts is brought under the series of brushes or contacts C, and by following the connections it will be seen/that when contacts C bear upon contacts K the motor will be supplied at the number of points requisite for producing four poles. On the other hand, when contacts (7 and L are brought together and the fOIUBI connections broken the motor willv be supplied at the number of points which will produce two poles.

The construction of the controller way ordinarily be greatly varied and either set of contacts made movable while the other is fixed, or both may be fixed and ordinary devices for bridging them employed. It is also obvious from a consideration of the principle having an invariable number of poles, and I which is therefore a constant-speed motor,

for the purpose of securing with a uniformlydistributed winding the advantages of a winding which is non-uniformly distributed. The saving of power in starting, stopping, or retarding the loadwhich is secured by the use of my invention will be easily seen. In starting from rest or in coming to a higher speed from a lower the speed rises as the number of poles is decreased, and since the motor will for each number of poles take ap; proximately only enough power to bring" its! speed to synchronism the power consumed at the lower synchronous speeds isless than that required when running at full or normal speed. So in retarding the load if when running at a higher'speed' thenumber of poles be increased the motor, driven by the inertia of the load at a rate-above-synchronism for the (new nun-her of poles, will act as a generator and deliver current to the lineuntil the s eed hasbeen reduced-'to synchronism. Simi arlv the potential energy of the load may be utilized to drive the motor as a generator, and so return power to the suppl -circuit.

'lhe ITBlJllOCl herein disclosec I-do not claim in this application, but do so. broadly in my copending application, filed December '3, 1906;

Having now described my invention, what I claim is 1. In a system of power transmission, the combination with a polyphase source, of a motor, havingv leads for a number of phases greater than that of the supply circuit, one or more transformers intermediate tothe supply-circuit and motor, and arranged to produce phases of the number required for the ureter and of different voltages, and means for connecting the transformer with the motor-circuits at points to produce different numbers of poles inthe motor, as set forth.

Ina system of power transmission, the pombination with a polyphase. source, of a motor having leads for a number of phases greater than that of the supply-circuit and for as great a number of pairs of poles as correspond to the lowest s eed at which the/motor is to be 0 crate one or more transformers interme iate to the sup lycircuit and motor, and arranged to pro uce phases of the number required for the motor and of the requisite dillerent voltages, and means for connecting the transformer with the motor-circuits in different orders according to the number of poles and voltage desired, as set forth.

3. In a system of power transmission, the combination with a olyphasesource, of a motor having leads tiom its winding for a number of phases greater than thaf of the supply-circuits, and for asgreat a number of? poles as corresponds to the lowest speed at otor beoperated, one or conneetedso "as to produce phases of the number required by the motor and of volwithif fferent numbers of pairs of poles, and j a ,ico ntroller' for changing J ;nections f between the with difierent numbers of pairs of poles from transformer-leads of voltages proper for such numbers, as set forth.

motor and transcombination with a-Jpol induction-motor, havin of phasesjgreater than tl iat of the supply-cirf.cu i t,'."'on'e or more transformers intermediate 0" the supply-circuit and motors, and ar anged tdprodjhcefphases of-the number require'dfor the? motor and of different vol-' hase source, of an formerwith the motor-circuits at points. to

. produce diflerent numbers] of poles in the f new, as set forth.

5. In a system of power transmission, the

bombinationwith apolyphase source, an induration-motor having leads for a number ofphases greater than that of the supply-circuit andfor as great a number of pairs of poles as which the motor, ist'o be operated, one or more transformers'intermediate to the sup lycircuit and motor, and arra ed to pro uce phases of the number require for the motor and of the'requisite different voltages, and nlileans for connecting the transformer with t e ing to thefnumber of poles and voltage desired, as setforth.

6. In a system of power transmission, the combination with a polyphase source, of an induction-motor having leads; from its winding for a number of phases greater than that of the sup ly-circuits, and for as great a number of po es as corresponds to the lowest 1 speed atwhich the motor is to be operated,

one ormoret'ransformers intermediate to the supply-circuit and motor and disposed or interconnected so as. to produce phases of the number required by the motor and of vdltages proper for. the operation of the motor with different numbers of pairs of poles, and a controller for changing the order of connecf tions between the motor and transformertermediate to the supply-circuit and motors,

Y A, eformers intermediateto thesup-E ply, ircuitv andn'lotor and disposed or inter ",tag'es f roper for the operation of the motor theorder of 0011-, uniformly-wound motor er-leads whereby the motor may be run 4. In a system of power transmission, theeads for a number ,t'age's," and means for connecting the trans-1,

correspond to the lowesf speed at motor-circuitsin different orders acco rd.

leads whereby the motor may be run with tages, and means for connecting the transformer with the motor-circuits at points to produce'different numbers ofpoles in the mo tor, as set forth. l

8. In a system of power transmission, the combination with a pol hase source; ofa

number of phases eater than that of the supply-circuit and or as great a'number of pairs of poles as correspond to the lowest speed at. which the motor is to be operated,

one or more transformers intermediate to the sup ly-circuit and motor, and. arranged to pro uce phases of the number required for ,the motor and of the requisite different voltages, and means for connecting the transformer with the motor-circuits in different orders according to the number of poles and voltage desired, as set forth;

9. In a system of power transmission, the, combination with a poly hase source, of a uniformly-wound motor avinlg1 leads from its winding for a number of p ases greater than that of the supply-circuits, and for as great a number of poles as corresponds to the lowest speed at which the motor is to be operated, one or more transformers intermediate to the supply-circuit and motor and disposed or interconnected so as to produce phases of the number re uired by the motor and of voltages roper or the operationof the motor with iffcrent numbers of pairs of poles, and a controller for changing the order of connections between the motor and transformer-leads whereby the motor may berun with different numbers of pairs of poles from transformer-leads of Voltages proper for such numbers, asset forth. i

10. In a system of power transmission, the combination with a olyphase source, of a uniformly-wound indiictwmmotor, having leads for a. number of phases greater than that of the supply-circuit, one or more transformers intermediate to the supply-circuit and motors, and arran ed to produce phases of the number require for the motor and of' different voltages, and means for connecting the transformer with the motor-circuits at points to produce different numbers of poles in the'motor, as set forth. I 11. In a system of power transmission, the

combination with a polyphase source, a uniformly-Wound induction-motor having leads for anumber of phases greater than that of the supply-circuit-and for as great a number v of pairs oflpoles as correspond tothe lowest speed at w ich the motor is to be 0 erated, one or more transformers intcrme iate to the supply-circuit and motor, and arranged to produce phases of the number re uired for the motor and of the requisite di erent aving leads for a voltages, and means for connecting the transformer with the motor-circuits in different orders according to the-number ofpoles and voltage desired, as set forth.

12. In a system of power transmissiomthe combination with a polyphasesource, of a uniformly'wound induction-motor having leads from its winding for a number of phases greater than that of the supply-circuits, and for as reat a number of poles as corresponds to the owest speed at which the motor is to be operated, one or more transformers intermediate to thegsupply-circuit ancl motor and disposed or interconnected so as to produce phases of the number required by the motor and of voltages pro or for the operation of the motor with di erent numbers of pairs of poles, and a controller for changing tl-c order of connections between the motor and transformer-leads whereby the motor may be run with different numbers of pairs of poles from transformer-leads of voltages proper for such numbers as set forth.

13. In a: system of power transmission, the combination of an alternating-current motor, leads thereto for a number of phases suflicient to give an approximately uniformnotating field with a uniform winding, and,

means for varying the number of poles Without varying the number of phases, as set forth.

leads for a number of phases suflicient to give an approximately uniform rotating field with a uniform Winding, leads. for o crating with different numbers of poles, an imeans for-varying the connections to alter tlienumber of poles without altering thenumber'of phases, as set forth.

. 15. In asystem of power transmission, the combination of a source of pol'yphaee alternating currents, line-wires transmitting the same, a motor having leads for a larger numbar of phases than could betransmitted-by' .the number of line-wires from the generator,

transformers between the generator and motor, and connections from the motor for varying the number of poles Without varying. the number of phases, as set forth.

16. In a system of power transmission, the

combination of an alternating-current inducti onmotor havin a uniform primary winding, groups-of lea s for giving'difieront'numbers of poles, each group having a numberof leads to receive a number 0t phases which will give a practically uniform rotating'field, and means for changing the connections of the leads to a su ply-circuit to increase or decrease the. num er of poles for dGOIQB-SII1.L' or increasing the speed ofthe'motonas sc-i forth. 7

' RALPH D; MERSHON. 1

Witnesses:

S; S. DUNHAM, M. LAWS ON DYER. 

